Re: [CAD_CAM_EDM_DRO] conversion of old nc to new drives

doveknives@... wrote:

>I have an older Tree Journeyman two axis knee mill that was set up to take some sort of cassette reader using somesort of magnetic tape cassette instead of punched tape. THis may have been a common drive at one time but it is the first one that I've seen.
>

This may have been for loading the "executive" or diagnostic and
maintenance programs, more
than for moving toolpath programs around. Many of these 2nd generation
CNC machines used
"DNC", distributed numeric control, where a central "mainframe" computer
held all the tool
programs and downloaded them by serial link as called for by the CNC
machines.

If the cassette drive is in a small box, maybe about an 8" cube,
however, this is often called
a "BTR", for behind the (paper tape) reader. Machines which didn't have
the DNC
capability, or rarely had their tool programs changed were often set up
this way, with one
portable BTR box that was brought out from the engineering office with
the toolpath
loaded on a cassette (or later a floppy). Some of them literally faked
the paper tape
with LEDs on a wand that was inserted into the read head. Others
plugged into the
paper tape reader port on the CNC, because this was a well-established
standard, I
think it is RS-374.

> Anyway, the boards are faulty and I get a malfuntion message on the screen. I've checked with the service guy Tree recommended to me and he told me that the boards are not available. He did how ever state that I could conver it to using the x & y feeds as simple power feeds to use the mill ans a standard manual mill if I desired. I would like however to see if there is anyway to conver this machine to operate off a PC and still use the factory installed x&y axis motors and encoders. Can anyone help me with advice on how to do this?
>
>

Yes, certainly. You need to establish what the motors are. I'm
suspecting this is a servo
machine, not stepper. That is actually good, as you can get better
performance with
servos. Secondly, you need to check what the position feedback
mechanism is.
Do you know that it is a digital shaft encoder? What voltage does it
take, and what
signal voltage does it provide?

Are the ballscrews in good shape?

Finally, you need to decide whether pseudo-servos (no position feedback
to computer)
such as Gecko or Rutex will do, or if you want a true servo system with
position feedback
to the computer, so if you move the machine manually, it shows up on the
screen.
(If you have handwheels, this makes it possible to use the machine as a
manual with
DRO, or CNC at the push of a button.)

There is more choice of software available for the pseudo-servo
approach, as these
drives take step and direction signals. But, EMC supports the true
servo mode also.
It runs under the real-time Linux operating system, which scares some
people off.
It can all be installed from one CD, however, and is an excellent
interpreter, with
tool length and tool radius compensation, very deep look-ahead and
smoothing, and
high block processing speeds. I've been running a full-servo conversion
with EMC
since 1999, and am pretty satisfied with it.

Jon